Activity: Agar and Carageenan
By Tey YI Shen
Linked fromACTIVITY
1.. Think about the chemical structure of carrageenan and agar - what do they have in common? Agar, kappa and iota carageenan are gelling gum. They form gel on cooling. Molecules undergo a coil-helix transition followed by aggregation of helices. Both are derived from red algae.
2. What are the differences between kappa, iota and lambda carrageenan? Why? The structures of these hydrocolloids are different. Percentage of sulphate content: Kappa carrageenan—25% Iota carrageenan—32% Lambda caregeenan—35% Thus, they are different in cation concentration. The higher the sulphate content, the lower the concentration of cation concentration. The net charge of them affect their protein reactivity. The gelation temperature also depends on the concentration of cation. All of them are hot soluble . but in cold water, they depend on the cation concentration. Lambda carageenan is very soluble in cold water, but kappa carageenan is not, unless with the aids of sodium salt. Kappa, iota carrageenan are thermoreversible whereas lambda caregeenan is thermoirreversible. Kappa, iota carrageenan gel upon cooling of hot aqueous solution containing salts. Lambda caregeenan does not jellify (only act as thickening agent) as it is soluble in cold water.
By Tey YI Shen
Linked fromACTIVITY
1.. Think about the chemical structure of carrageenan and agar - what do they have in common?
Agar, kappa and iota carageenan are gelling gum. They form gel on cooling. Molecules undergo a coil-helix transition followed by aggregation of helices. Both are derived from red algae.
2. What are the differences between kappa, iota and lambda carrageenan? Why?
The structures of these hydrocolloids are different.
Percentage of sulphate content:
Kappa carrageenan—25%
Iota carrageenan—32%
Lambda caregeenan—35%
Thus, they are different in cation concentration. The higher the sulphate content, the lower the concentration of cation concentration.
The net charge of them affect their protein reactivity.
The gelation temperature also depends on the concentration of cation.
All of them are hot soluble . but in cold water, they depend on the cation concentration. Lambda carageenan is very soluble in cold water, but kappa carageenan is not, unless with the aids of sodium salt.
Kappa, iota carrageenan are thermoreversible whereas lambda caregeenan is thermoirreversible.
Kappa, iota carrageenan gel upon cooling of hot aqueous solution containing salts. Lambda caregeenan does not jellify (only act as thickening agent) as it is soluble in cold water.